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Bromatometry for Pharmacists

This document discusses the principles and applications of bromatometry, which is a titration method using potassium bromate. Potassium bromate is a powerful oxidizing agent that is reduced to bromide and then oxidizes bromide to form free bromine. The equivalent amount is 1/6 moles of potassium bromate. One application is the assay of isoniazid, an anti-tubercular drug, where potassium bromate is used to titrate and release bromine, which then reacts with isoniazid. The procedure involves weighing isoniazid and titrating with a standardized solution of potassium bromate while using an indicator.

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1K views1 page

Bromatometry for Pharmacists

This document discusses the principles and applications of bromatometry, which is a titration method using potassium bromate. Potassium bromate is a powerful oxidizing agent that is reduced to bromide and then oxidizes bromide to form free bromine. The equivalent amount is 1/6 moles of potassium bromate. One application is the assay of isoniazid, an anti-tubercular drug, where potassium bromate is used to titrate and release bromine, which then reacts with isoniazid. The procedure involves weighing isoniazid and titrating with a standardized solution of potassium bromate while using an indicator.

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BROMATOMETRY (Potassium-Bromate titration)

PRINCIPLE: Potassium Bromate is a powerful oxidizing agent which is reduced smoothly to


bromide in the presence of HCl and which is then oxidized to give free bromine by bromate
(excess).

BrO3- + 6H+ + 6e- Br- + 3H2O

BrO3- + 5Br- + 6H+ 3Br2 + 3H2O

The equivalent is therefore 1/6 moles, KBrO 3 /6 or 167/6 which is equal to 27.88 . At the end point
of titration free bromine appears.

BrO3- + 5Br- + 6H+ 3Br2 + 3H2O therefore,

KBrO3 + 5Br- +6HCl. 3Br2. + 6KCl + 3H2O

PREPARATION OF 0.016M KBrO 3 SOLUTION: Potassium bromate is usually available in a


high state of purity. The anyalytical reagent product has an assay value of 99.9%. The substance can
be dried at 120-150˚ is anhydrous and the aqueous solution keeps it indefinitely, it can therefore be
employed as a primary standard. Its only disadvantage is that 1/6th of the relative molecular mass is
a Comparatively small quantity.

PREPARATION: Dissolve 2.783gm of KBrO 3 in sufficient quantity of water to produce 1000ml.

APPLICATIONS:
1. Assay of Isoniazid
2. Determination of Hydroxylamine
3. Determination of As/Sb

ASSAY OF ISONIAZID IP : Anti-tubercular drug. This is determined by addition of potassium


bromide and direct titration of potassium bromate in the presence of HCl solution. Bromine is
released as the titration proceeds and reacts with isoniazid as shown below the Azo-dye, methyl red
solution is used as an indicator which decolorises by oxidation at end point.

KBrO3 + 5Br- + 6HCl 3Br2. + 6KCl + 3H2O

PROCEDURE FOR ASSAY: Weigh accurately about 0.25gm in sufficient water to produce
100ml. From this solution take 20ml and add 100ml water, 20ml HCl and 0.2gm of KBr and titrate
slowly with continuous shaking with 0.016M KBrO3 solution using 0.05ml of methyl red solution
as indicator until the red color disappears.

IP FACTOR: Each ml of 0.016M KBrO3 solution = 0.003429gm of Isoniazid (C6H7N3O).

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